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ATLAS in the LHC collision era

ATLAS in the LHC collision era. M.Bosman IFAE - Barcelona on behalf of the ATLAS Collaboration IMFP 2010 – La Palma. Effort of the ATLAS Worldwide Scientific Community for > 20 years. ~ 2900 scientists (~1000 students), 172 Institutions, 37 countries. ATLAS Detector. 45 m. 24 m. 7000 T.

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ATLAS in the LHC collision era

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  1. ATLAS in the LHC collision era M.Bosman IFAE - Barcelona on behalf of the ATLAS Collaboration IMFP 2010 – La Palma

  2. Effort of the ATLAS Worldwide Scientific Community for > 20 years ~ 2900 scientists (~1000 students), 172 Institutions, 37 countries ATLAS, M.Bosman, IFAE

  3. ATLAS Detector 45 m 24 m 7000 T ATLAS, M.Bosman, IFAE

  4. Inner Detector Tracking ||<2.5 B=2T Silicon pixels (Pixel): 0.8 108 channels Silicon strips (SCT) : 6 106 channels Transition Radiation Tracker (TRT) : straw tubes (Xe), 4 105 channels e/ separation /pT ~ 5x10-4 pT  0.01 ATLAS, M.Bosman, IFAE

  5. Calorimetry Calorimetry ||<5 Hadron Calorimeter barrel Iron-Tile EC/FwdCu/W-LAr (~20000 channels) /E ~ 50%/E  0.03 pion (10 ) Trigger for e/γ , jets, Missing ET Electromagnetic Calorimeter barrel,endcap: Pb-LAr ~10%/√E energy resolution e/γ 180000 channels: longitudinal segmentation ATLAS, M.Bosman, IFAE

  6. Stand-alone momentum resolution Δpt/pt < 10% up to 1 TeV Muon System 2-6 Tm ||<1.3 4-8 Tm 1.6<||<2.7 ~1200 MDT precision chambers for track reconstruction (+ CSC) ~600 RPC and ~3600 TGC trigger chambers ATLAS, M.Bosman, IFAE

  7. People are happy again... A key date for ATLAS in 2009 ATLAS, M.Bosman, IFAE

  8. LHC went very quickly from circulating beams to collisions at √s =900 GeV • Friday 20 November: • Circulating beams • “Beam splashes” • Monday 23 November: • first collisions at √s = 900 GeV ! • ATLAS records ~ 200 events • (first one observed at 14:22) ATLAS, M.Bosman, IFAE

  9. Sunday 6 December: machine • protection system commissioned • stable (safe) beams for first time • full tracker at nominal voltage • whole ATLAS operational ATLAS, M.Bosman, IFAE

  10. ATLAS, M.Bosman, IFAE

  11. 8, 14, 16 December: collisions at √s = 2.36 TeV (few hours total) • ATLAS records ~ 34000 events ATLAS, M.Bosman, IFAE Jet1: ET (EM scale)~ 16 GeV, η= -2.1 Jet2: ET (EM scale) ~ 6 GeV, η= 1.4

  12. Detector is fully operational • Pixels and Silicon strips (SCT) at nominal voltage only with stable beams • Solenoid and/or toroids off in some periods • Muon forward chambers (CSC) running in separate partition for rate tests ATLAS, M.Bosman, IFAE

  13. Let’s go back in time..... Cosmic Muon Runs • 216 Million Cosmics in Sep/Oct 2008 • 90 Million Cosmics in Jun/Jul 2009 • 266 Million Cosmics in Oct/Nov 2009 ATLAS, M.Bosman, IFAE

  14. 2008 Cosmics Data Cosmic Muon Runs Cosmics-Muon-Runs useful for initial detector calibration, operation experience, ... some examples alignment of SCT efficiency of MDT tubes ATLAS, M.Bosman, IFAE

  15. Beam Splashes Cosmics-Muon-Runs useful for initial detector calibration, operation experience, ... a couple of examples Muon Chambers Timing Synchronize all chambers at a given z using the synchronous front of splash particles and the very large particle flux Calorimeter energy calibration ET Level-1 trigger versus offline reconstruction Calorimeter Timing After 2008 beam-splash data taking and analysis of many millions of cosmics events, timing good within a few ns ATLAS, M.Bosman, IFAE

  16. Recorded data samplesNumber of Integrated luminosity events (< 30% uncertainty) Total ~ 920k ~ 20 μb-1 With stable beams ( tracker fully on) ~ 540k ~ 12 μb-1 At √s=2.36 TeV ~ 34k ≈ 1 μb-1 Recorded data samples Average data-taking efficiency: ~ 90% ATLAS, M.Bosman, IFAE

  17. Measuring luminosity scintillators in front of endcap example: run with 4hours of stable beam forward luminosity monitor (22 m / in front of quadrupole) LAr endcaps overall systematic uncertainty up to 30%. Max peak luminosity seen by ATLAS : ~ 7 x 1026 cm-2 s-1 ramping-up Silicon Detector after stable-beam signal ATLAS, M.Bosman, IFAE

  18. Trigger/DAQ Architecture ROIB L2SV DFM ROD ROD ROD ROB ROB ROB L2N L2P EBN SFI EFN EFP SFO Infrastructure Control & Monitoring Communication Databases DAQ Trigger Calo MuTrCh Other detectors LVL1 40 MHz 2.5 ms Det. R/O 140M Channels LVL1 accept (75 kHz) RoI Dataflow 150 nodes High Level Trigger ~40 ms LVL2 ROS 500 nodes RoI requests RoI data (~2%) EB 100 nodes LVL2 accept (~3 kHz) 1800 nodes ~4 sec EF ~100 nodes EF accept (~0.2 kHz) ATLAS, M.Bosman, IFAE

  19. High-Level Trigger in rejection mode (in addition, running > 150 chains in pass-through) Collision trigger (L1) Scintillators (Z~± 3.5 m): rate up to ~ 30 Hz Trigger Online determination of the primary vertex and beam spot using L2 trigger algorithms Spot size ~ 250 μm ATLAS, M.Bosman, IFAE

  20. Worldwide data distribution and analysis MB/s per day Total data throughput through the Grid (Tier0, Tier-1s, Tier-2s) End of data taking Nov. Dec. Beam splashes First collisions Cosmics • ~ 0.2 PB of data stored since 20th November • ~ 8h between Data Acquisition at the pit and data arrival at Tier2 • (including reconstruction at Tier0) • increasing usage of the Grid for analysis WLCG ATLAS, M.Bosman, IFAE

  21. Collisions - Inner Detector ATLAS, M.Bosman, IFAE

  22. p 180k tracks K π Inner Detector - Pixel The dE/dx is measured per track as the mean of the cluster charge properly weighted for the track length in silicon. 180k tracks (3 Pixel Hits)  10% of data Track momentum X charge Q Pixel cluster width as a function of the track incident angle in Rphi direction ATLAS, M.Bosman, IFAE

  23. Inner Detector - SCT Silicon strips Intrinsic module efficiency for tracks measured in the SCT Barrel (dead modules and chips are taken into account). Lorentz angle extracted from the cluster-size vs angle compared to model prediction. ATLAS, M.Bosman, IFAE

  24. straw Anode wire Xe Foil Inner Detector - TRT Transition Radiation Tracker HV - • Energy of TR photons (proportional to 1-2): • ~ 10-30 keV (X-rays) • Many crossings of polypropylene foils (radiator) to increase TR photons • Xenon as active gas for high X-ray absorption electron from photon conversion reconstructed in ID with tight identification in calorimeter Transition radiation intensity is proportional to particle relativistic factor γ=E/mc2. Onset for γ ~ 1000 ATLAS, M.Bosman, IFAE all tracks

  25. Reconstructingdecays pT (track) > 100 MeV MC signal and background normalized independently ATLAS, M.Bosman, IFAE

  26. K0S Λ Reconstructingdecays ATLAS, M.Bosman, IFAE

  27.   e+e-conversions pT (e+) = 1.75 GeV, 11 TRT high-threshold hits pT (e-) = 0.79 GeV, 3 TRT high-threshold hits e- γ conversion point R ~ 30 cm (1st SCT layer) e+ ATLAS, M.Bosman, IFAE

  28. Calorimeter – cell signals cell signal in randomly triggered events LAr calorimeter cell signal in collision events ATLAS, M.Bosman, IFAE

  29. Calorimeter – photons : π0 γγ π0 γγ Data and MC normalised to the same area • 2 photon candidates with ET (γ) > 300 MeV • ET (γγ) > 900 MeV • Shower shapes compatible with photons • No corrections for upstream material applied ATLAS, M.Bosman, IFAE

  30. Calorimeter – photons Photon candidates: shower shape in the EM calorimeter Soft photons ! Challenging because of material in front of EM calorimeter (cryostat, coil): ~ 2.5 X0 at η=0 ATLAS, M.Bosman, IFAE

  31. E (cluster) / p (track) Calorimeter – Electron candidates EM clusters ET > 2.5 GeV matched to a track  783 candidates in 330k minimum-bias events Data and MC normalised to the same area ET spectrum • According to MC: • Sample dominated • by hadron fakes • Most electrons from • γ-conversions Good data-MC agreement for (soft !) electrons and hadrons Transition radiation hits in the TRT (transition radiation from electrons produces more high-threshold hits) ATLAS, M.Bosman, IFAE

  32. Calorimeter – Isolated hadron response |η| < 0.8, 0.5 < pT < 10 GeV Cluster energy at EM scale Monte Carlo and data normalized to same area Good agreement in the (challenging) low-E region indicates good description of material and shower physics in Geant4 simulation Years of test-beam, collaboration with Geant4 team ATLAS, M.Bosman, IFAE

  33. √s=2.36 TeV √s=2.36 TeV Calorimeter - Jets Jets √s=900 GeV ATLAS, M.Bosman, IFAE

  34. Calorimeter - Jets Uncalibrated EM scale jets with pT>7 GeV Monte Carlo (Non Diffractive Minimim Bias) normalized to number of jets or events in data Events with2 jets with pT> 7 GeV ATLAS, M.Bosman, IFAE

  35. Calorimeter – Missing Transverse Energy METx / METy = x/y components of missing ET vector METy METx • Sensitive to calorimeter performance (noise, coherent noise, dead cells, mis-calibrations, • cracks, etc.) and backgrounds from cosmics, beams, … • Measurement over full calorimeter coverage (3600 in φ, |η| < 5, ~ 200000 cells) ATLAS, M.Bosman, IFAE

  36. Calorimeter – Missing Transverse Energy METx ATLAS, M.Bosman, IFAE

  37. Collisions: a physics Roadmap Higgs discovery sensitivity (MH=130~500 GeV) Explore SUSY to m ~ TeV Precision SM measurements 100 Sensitivity to 1-1.5 TeV resonances → lepton pairs Understand SUSY and Higgs background from SM More accurate alignment & EM/Jet/ETmiss calibration 10 Integrated Luminosity (a.u.) 1 Search for very striking new physics signature Use SM processes as “standard candles” Initial detector & trigger synchronisation, commissioning, calibration & alignment, material Test beam, cosmic runs, pre-alignment & calibration, extensive simulations ... time ATLAS, M.Bosman, IFAE

  38. Example of first signals 1 pb-13 days at 1031at 30% efficiency After all cuts: ~ 5000 (800) J/ (Y)  / day @ L = 1031 cm-2 s-1 (for 30% machine x detector data taking efficiency) (at 7 TeV reduced by ~x2) J/  tracker momentum scale, trigger performance, detector efficiency, sanity checks, … Y1S 14 TeV Initial robust analysis e10 trigger loose identification background extrapolated from side bands 50 pb-1 ATLAS After all cuts: ~ 160 Z ee day at L = 1031 cm-2 s-1 energy/momentum scale of full detector Muon Spectrometer alignment, lepton trigger and reconstruction efficiency, … ~25 k events for 50 pb-1 at 14 TeV (at 7 TeV reduced by ~x2) quickly dominated by systematic ATLAS, M.Bosman, IFAE

  39. W Trigger and offline efficiencies from tag-and-probe (Z) Muon isolation in calo Missing ET > 25GeV Ldt=50pb-1: 300k W, 20k bckgd events W/Z Production Z • Trigger and offline eff. from tag-and-probe • Tracks in Muon Spectrometer Ldt=50pb-1:26k Z, 0.1k bckgd evt ATLAS ATLAS 14 TeV at 7 TeV, about a factor 2 less signal events ATLAS, M.Bosman, IFAE

  40. Top production 3 jets pT> 40 GeV + 1 jet pT> 20 GeV PT(lep) > 20 GeV Missing ET > 20 GeV 10 TeV for 200 pb-1  channel 1600 events Signal, 800 Bck e channel: 1300 events Signal, 600 Bck No b-tagging at 7 TeV, signal reduced by factor 2.5 ATLAS, M.Bosman, IFAE ttbar pair production: semi leptonic decays

  41. Conclusions taken from F.Gianotti, ATLAS Spokesperson Report to CERN Council Dec 09 • ATLAS has successfully collected first LHC collision data. • The whole experiment operated efficiently and fast, from data taking at the pit, to data transfer worldwide, to the production of first results • (on a very short time scale … few days). • First LHC data indicate that the performance of the detector, simulation and reconstruction (including the understanding of material and control of instrumental effects) is far better than expected at this (initial) stage of the experiment and in an energy regime ATLAS was not optimized for. • Years of test beam activities, increasingly realistic simulations, and commissioning with cosmics to understand and optimize the detector performance and validate the software tools were fundamental to achieve these results. • The enthusiasm and the team spirit in the Collaboration are extraordinary. This is only the beginning of an exciting physics phase and a major achievement of the worldwide ATLAS Collaboration after > 20 years of efforts to build a detector of unprecedented technology, complexity and performance. ATLAS, M.Bosman, IFAE

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